In the related art, due to advancement of miniaturization of a pixel size, a technology of pixel sharing (pixel sharing technology) is more often adopted in a complementary metal oxide semiconductor (CMOS) image sensor in order to maximize an aperture ratio of a photo diode (PD). The pixel sharing technology is a technology to secure an aperture area of a photo diode by minimizing an occupying area of elements other than the photo diode in a pixel portion by sharing a transistor among a plurality of pixels. By using this pixel sharing technology, characteristics such as a saturation signal amount and sensitivity of a photo diode can be improved (refer to Patent Documents 1 to 4).
In the above-described structure, a layer formed with a transistor is formed as an epitaxial layer on a layer formed with the photo diode. Furthermore, as a method of transferring charge to a floating diffusion from a photo diode, adopted are a method of using a vertical transistor and an II plug method in which connection is made by ion implant (II).